The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Night owls linked to anti-social behaviour

Students who stay up late at night are more likely to display anti-social personality traits, according to new research.

The University of Western Sydney study shows students who stay awake into the early hours of the morning display greater anti-social tendencies than those who go to bed earlier.

Dr Peter Jonason, from the university's school of social sciences and psychology, assessed more than 250 people to find out whether being a night owl is linked to narcissism, Machiavellianism and psychopathic tendencies, often described as the dark triad of personality traits.

"Those who score highly on the dark triad traits are, like many other predators, creatures of the night," he says.

There may be an evolutionary basis for the link.

"There is likely to be a co-evolutionary arms race between cheaters and those who wish to detect and punish them, and the dark triad traits may represent specialised adaptations to avoid detection," he says.

The features of the night - a low-light environment where others are sleeping - may facilitate the casual sex, mate-poaching and risk-taking to which the dark triad traits are linked.

Dr Jonason says more work is needed, but the results represent an important advance in the study of the darker aspects of human nature and personality.

His study, The Creatures of the night: Chronotypes and the Dark Triad, is published in the journal Personality and Individual Differences.